Field of the Invention
The present invention relates to a position detection apparatus that detects a position of a target.
Description of the Related Art
There is a known image forming apparatus that primarily transfers toner images respectively formed on a plurality of photosensitive members to an intermediate transfer belt and secondarily transfers a color image composited on the intermediate transfer belt to a recording sheet.
Incidentally, when the intermediate transfer belt (a target) in the image forming apparatus is deviated (moves) in a width direction that intersects perpendicularly with a belt conveying direction, color misregistration in which the toner images of the plurality of colors on the intermediate transfer belt are deviated may occur. In order to prevent such color misregistration, a belt-deviation-amount detection technique that detects a deviation amount of the intermediate transfer belt in the width direction that intersects perpendicularly with the belt conveying direction is proposed.
As an apparatus that detects a deviation amount of an intermediate transfer belt, there is a known apparatus that is provided with a swinging arm of which one end is in contact with an edge of the intermediate transfer belt to swing and two transmission optical sensors disposed on the other end of the swinging arm, for example. This deviation amount detection apparatus detects the deviation amount of the belt corresponding to light amount variation due to change in a shield factor with using the fact that the shield factors of the two transmission optical sensors vary corresponding to the swinging angle of the swinging arm (for example, see U.S. Pat. No. 8,412,081).
However, the above-mentioned belt-deviation-amount detection technique cannot detect breakage (hereinafter referred to as failure) even if any one of the optical sensors used for detecting the deviation amount (moving amount) of the belt has broken. Then, if the position of the target is corrected on the basis of the erroneously detected position while one of the sensors fails, an error may occur or the target may break.